uBITx Control circuit...

K9HZ <bill@...>

I spent time over the last week designing a fool-proof control circuit for the uBITx for power control.  This circuit prevents bad things from happening by shutting down the radio before any damage is done.  It FAULTS on 1) over power, 2) High SWR, 3) High PA Current, and 4) High voltage.  It also protects against connecting the radio to the power backwards.  What I particularly like about it is that it provides a visual indication of WHAT fault occurred, and actually the individual fault LEDs begin to flicker BEFORE the trip so you can fix the problem before you hit a hard trip.  I the four trips I listed above can be expanded to any number by adding more SCR Trip components (they are set to trip at 1.8V whatever the fault is).  When initially turned on, the transistorized RS Flipflop circuit comes up in the “Operate” mode.  If a trip occurs, it flips into “FAULT” and shuts down the PA.  The circuit is reset with the “RESET” button, but ONLY if the fault has been resolved.  Turning the power off and on resets the circuit too.


I bread-boarded the circuit last week and have been using it on my radio for a while.  It works flawlessly (yes transmitting and yanking the coax off the back of the radio shuts down the PA nicely!).  I’ll post the circuit and a build list in the files section.  This is a public circuit so feel free to design and build boards if you want… I’m working on other things that I want to finish.





Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ


Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois


Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon


Moderator – North American QRO Yahoo Group.


email:  bill@...



Virus-free. www.avg.com

Join BITX20@groups.io to automatically receive all group messages.